AdventOfCode/AdventOfCode.Solutions/2023/Day 16/Day16.cs

using AdventOfCode.Core.Shared.IO;

namespace AdventOfCode.Solutions._2023
{
    public class Day16 : IChallange
    {
        public int Year => 2023;
        public int Day => 16;

        private readonly IInputReader _inputReader;

        public Day16(IInputReader inputReader)
        {
            _inputReader = inputReader;
            _inputReader.SetInput(this);
        }

        public async Task<string> GetSolutionPart1()
        {
            Grid<Point> grid = await _inputReader.ReadToGrid<Point>();
            Point? point = grid.TryGetNode(0, 0);
            ISet<Point> set = Move(grid, new HashSet<Point>(), new HashSet<Point>(), point, Direction.Right);
            return set.Count.ToString();
        }

        public async Task<string> GetSolutionPart2()
        {
            Grid<Point> grid = await _inputReader.ReadToGrid<Point>();
            int columnMax = grid.GetColumn(0).Select(p => Move(grid, new HashSet<Point>(), new HashSet<Point>(), p, Direction.Down).Count).Max();
            int rowMax = grid.GetRow(0).Select(p => Move(grid, new HashSet<Point>(), new HashSet<Point>(), p, Direction.Right).Count).Max();
            return Math.Max(columnMax, rowMax).ToString();
        }

        private static ISet<Point> Move(Grid<Point> grid, ISet<Point> energized, ISet<Point> splittersHit, Point? currentLocation, Direction direction) 
        {
            if (currentLocation == null)
                return energized;

            if ((currentLocation.Value == '-' || currentLocation.Value == '|') && !splittersHit.Add(currentLocation))
                return energized;

            energized.Add(currentLocation);


            (long X, long Y, Direction NewDirection) newPosition = (currentLocation.X, currentLocation.Y, direction);
            switch (currentLocation.Value)
            {
                case '.':
                    newPosition = MoveStraight(currentLocation, direction);
                    Point? newPoint = grid.TryGetNode(newPosition.X, newPosition.Y);
                    while(newPoint != null && newPoint.Value == '.')
                    {
                        energized.Add(newPoint);
                        newPosition = MoveStraight(newPoint, direction);
                        newPoint = grid.TryGetNode(newPosition.X, newPosition.Y);
                    }
                    return Move(grid, energized, splittersHit, grid.TryGetNode(newPosition.X, newPosition.Y), newPosition.NewDirection);
                case '\\':
                    if (direction == Direction.Down || direction == Direction.Up)
                        newPosition = MoveLeft(currentLocation, direction);
                    else if (direction == Direction.Right ||direction == Direction.Left)
                        newPosition = MoveRight(currentLocation, direction);
                    return Move(grid, energized, splittersHit, grid.TryGetNode(newPosition.X, newPosition.Y), newPosition.NewDirection);

                case '/':
                    if (direction == Direction.Down || direction == Direction.Up)
                        newPosition = MoveRight(currentLocation, direction);
                    else if (direction == Direction.Right || direction == Direction.Left)
                        newPosition = MoveLeft(currentLocation, direction);

                    return Move(grid, energized, splittersHit, grid.TryGetNode(newPosition.X, newPosition.Y), newPosition.NewDirection);
                case '|':
                    if (direction == Direction.Up || direction == Direction.Down)
                        newPosition = MoveStraight(currentLocation, direction);
                    else
                    {
                        newPosition = MoveLeft(currentLocation, direction);
                        energized = Move(grid, energized, splittersHit, grid.TryGetNode(newPosition.X, newPosition.Y), newPosition.NewDirection);
                        newPosition = MoveRight(currentLocation, direction);
                    }
                    return Move(grid, energized, splittersHit, grid.TryGetNode(newPosition.X, newPosition.Y), newPosition.NewDirection);
                case '-':

                    if  (direction == Direction.Right || direction == Direction.Left)
                        newPosition = MoveStraight(currentLocation, direction);
                    else
                    {
                        newPosition = MoveLeft(currentLocation, direction);
                        energized = Move(grid, energized, splittersHit, grid.TryGetNode(newPosition.X, newPosition.Y), newPosition.NewDirection);
                        newPosition = MoveRight(currentLocation, direction);
                    }
                    return Move(grid, energized, splittersHit, grid.TryGetNode(newPosition.X, newPosition.Y), newPosition.NewDirection);
            }   


            return energized;
        }

        private enum Direction
        {
            Up,
            Down,
            Left,
            Right
        }

        private static (long X, long Y, Direction NewDirection) MoveStraight(Point from, Direction direction)
        {
            return direction switch
            {
                Direction.Up => (from.X, from.Y - 1, direction),
                Direction.Down => (from.X, from.Y + 1, direction),
                Direction.Left => (from.X - 1, from.Y, direction),
                Direction.Right => (from.X + 1, from.Y, direction),
                _ => (from.X, from.Y, direction),
            };
        }

        private static (long X, long Y, Direction NewDirection) MoveLeft(Point from, Direction direction)
        {
            return direction switch
            {
                Direction.Up => (from.X - 1, from.Y, Direction.Left),
                Direction.Down => (from.X + 1, from.Y, Direction.Right),
                Direction.Left => (from.X, from.Y + 1, Direction.Down),
                Direction.Right => (from.X, from.Y - 1, Direction.Up),
                _ => (from.X, from.Y, direction),
            };
        }

        private static (long X, long Y, Direction NewDirection) MoveRight(Point from, Direction direction)
        {
            return direction switch
            {
                Direction.Up => (from.X + 1, from.Y, Direction.Right),
                Direction.Down => (from.X - 1, from.Y, Direction.Left),
                Direction.Left => (from.X, from.Y - 1, Direction.Up),
                Direction.Right => (from.X, from.Y + 1, Direction.Down),
                _ => (from.X, from.Y, direction),
            };
        }
    }
}